Thermo-Hydrogen Refinement of Microstructure of Titanium Materials

ABSTRACT

A method of refining a microstructure of a titanium material can include providing a solid titanium material at a temperature below about 400° C. The titanium material can be heated under a hydrogen-containing atmosphere to a hydrogen charging temperature that is above a β transus temperature of the titanium material and below a melting temperature of the titanium material, and held at this temperature for a time sufficient to convert the titanium material to a substantially homogeneous β phase. The titanium material can be cooled under the hydrogen-containing atmosphere to a phase transformation temperature below the β transus temperature and above about 400° C., and held for a time to produce α phase regions. The titanium material can also be held under a substantially hydrogen-free atmosphere or vacuum at a dehydrogenation temperature below the β transus temperature and above the δ phase decomposition temperature to remove hydrogen from the titanium material.

RELATED APPLICATIONS

This application is a continuation of U.S. Application No. 17/485,882,filed Sep. 27, 2021, which is a continuation-in-part of U.S. ApplicationNo. 17/177,039, filed Feb. 16, 2021, which is a continuation of U.S.Application No. 16/154,536 (now issued as U.S. Pat. No. 10,920,307),filed Oct. 8, 2018 which claims priority to U.S. Provisional ApplicationNo. 62/569,294, filed Oct. 6, 2017, which are each incorporated hereinby reference.

BACKGROUND

Titanium alloys can have high specific strength, excellent corrosionresistance, and great biocompatibility. Due to these properties,titanium alloys may have profound implications for sustainability ifmade economical for widespread commercial utilization. Wider use ofthese materials can significantly improve energy efficiency inapplications such as the automotive industry and power generation byreducing the weight of high-strength components. Making these componentsfrom titanium materials can also provide significantly increased servicelife. However, the traditional processes for making high-performancetitanium materials, such as wrought processing, are highlyenergy-intensive, making these materials unfeasible for most commercialapplications outside of aerospace and biomedicine. Furthermore, the millproducts produced by wrought processing can only be made in simplegeometries, such as plate, sheet, and bar stock. Therefore, producingend-user components typically requires extensive machining, forming,joining, etc., which further increase the embodied energy by increasingthe amount of energy required for production and limiting overall yieldthrough material losses.

Near-net-shape production technologies, such as casting and additivemanufacturing (AM, e.g. 3D printing), have been identified as a means tosignificantly improve the economics of using titanium alloys for a widevariety of applications. Such processes avoid the energy-intensivethermomechanical processing (TMP) employed by wrought processing.Additionally, these technologies can directly produce complexgeometries, which allows for significant reduction in the amount ofsubsequent machining, forming, joining, etc., required. Furthermore, AMhas many more benefits in regards to rapid prototyping and directdigital manufacturing. However, despite these benefits, using manynear-net-shape technologies significantly compromises the resultingmechanical performance of the titanium alloy components.

For the most common α+β titanium alloy (i.e. Ti-6Al-4V), casting andelectron beam AM (e.g. electron beam melting, etc.) can produce a coarselamellar microstructure with limited strength and poor fatigueperformance. Conversely, laser AM (e.g. direct metal laser sintering,selective laser melting, etc.) can produce a highly acicular/martensiticmicrostructure with poor ductility and highly anisotropic mechanicalproperties. As aforementioned, TMP is the traditional route forengineering titanium alloy microstructures and producing highperformance mechanical properties. However, utilizing TMP would bothincrease the embodied energy of the material and, more importantly,sacrifice the near-net-shape capability of these technologies.Therefore, there has long been a need for a process that can refine themicrostructure of titanium alloys in an energy efficient manner andwithout requiring any deformation.

SUMMARY

The present invention involves methods of refining the microstructure oftitanium materials. In one example, a method of refining amicrostructure of a titanium material can include providing a solidtitanium material at a temperature below about 400° C. The titaniummaterial can be heated under a hydrogen-containing atmosphere to ahydrogen charging temperature. The hydrogen charging temperature can beabove a β transus temperature of the titanium material and below amelting temperature of the titanium material. For all titaniummaterials, the β transus temperature can change with hydrogen content,which can be considered when determining the appropriate hydrogencharging temperature. The titanium material can be held at thistemperature for a hydrogen charging time sufficient to convert thetitanium material to a substantially homogeneous β phase titaniummaterial. The method can also include cooling the titanium materialunder the hydrogen-containing atmosphere to a phase transformationtemperature. The phase transformation temperature can be below the βtransus temperature and above about 400° C. The titanium material can beheld at the phase transformation temperature for a phase transformationtime to produce regions of the lower temperature α, α₂, and in somecases δ phases. Further, the method can include holding the titaniummaterial under a substantially hydrogen-free atmosphere or vacuum at adehydrogenation temperature to form a dehydrogenated titanium material.The dehydrogenation temperature can be below the β transus temperatureof the hydrogen-free titanium material and above the decompositiontemperature of the δ phase, about 200° C. for some alloys. This canremove at least a portion of hydrogen from the titanium material.

The present technology also extends to titanium materials having refinedmicrostructures that can be made through the processes described herein.In one example, a titanium material can have a microstructure includingprior β grains with an average diameter ranging from about 50 µm to over1000 µm that form at the hydrogen charging temperature. Within theboundaries of the prior β grains, the titanium material can haveultrafine lamellar α grains with average lengths ranging from 5 µm to 8µm and average widths ranging from 0.1 µm to 2 µm. Further, these αgrains can be arranged into colonies that have average lengths rangingfrom 5 µm to 8 µm and average widths ranging from 1 to 4 µm. Thematerial can also have a layer of α grains with average widths of 2 µmto 6 µm along the boundaries the prior β grains. Thus, in some examples,prior β grains can be 10 to 400 times, and in some cases up to 200 timeslarger than α grain colonies. Similarly, α grain widths of grainboundary α grains can be within 50%, and often within 10% of an averagediameter of the α grain colony.

There has thus been outlined, rather broadly, the more importantfeatures of the invention so that the detailed description thereof thatfollows may be better understood, and so that the present contributionto the art may be better appreciated. Other features of the presentinvention will become clearer from the following detailed description ofthe invention, taken with the accompanying drawings and claims, or maybe learned by the practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of an example method of refining a microstructureof a titanium material.

FIG. 2 is a graph of temperature vs. time for another example method ofrefining a microstructure of a titanium material.

FIG. 3 is a phase diagram in terms of temperature vs. hydrogen contentalso showing stages in another example method of refining amicrostructure of a titanium material.

FIG. 4 is a cross-sectional view of a microstructure of an exampletitanium material produced using the present methods.

FIG. 5 is a cross-sectional view of a microstructure of another exampletitanium material produced using the present methods.

FIG. 6 is a cross-sectional view of a microstructure of another exampletitanium material produced using the present methods.

These drawings are provided to illustrate various aspects of theinvention and are not intended to be limiting of the scope in terms ofdimensions, materials, configurations, arrangements or proportionsunless otherwise limited by the claims.

DETAILED DESCRIPTION

While these exemplary embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, it should beunderstood that other embodiments may be realized and that variouschanges to the invention may be made without departing from the spiritand scope of the present invention. Thus, the following more detaileddescription of the embodiments of the present invention is not intendedto limit the scope of the invention, as claimed, but is presented forpurposes of illustration only and not limitation to describe thefeatures and characteristics of the present invention, to set forth thebest mode of operation of the invention, and to sufficiently enable oneskilled in the art to practice the invention. Accordingly, the scope ofthe present invention is to be defined solely by the appended claims.

Definitions

In describing and claiming the present invention, the followingterminology will be used.

As used herein, “titanium material” can include titanium metal andalloys of titanium with other elements. In certain non-limiting specificexamples, the titanium material can be commercially pure (CP) titaniummetal, Ti-6Al-4V, Ti-6Al-6V-2Sn, Ti-0.3Mo-0.8N, Ti-3Al-2.5V,Ti-5Al-2.5Sn, Ti-0.15Pd, Ti-3Al-8V-6Cr-4Mo-4Zr, and the like. TheTi-6Al-4V alloy refers to an alloy that consists essentially of about 6wt% aluminum, about 4 wt% vanadium, and the remainder being titanium.These proportions are approximate and in some examples the amounts canvary. For example, the amount of aluminum can be from 5.5 wt% to 6.75wt% in some examples. The amount of vanadium can be from 3.5 wt% to 4.5wt% in further examples. The alloy can also include impurities of smallamounts of other elements, such as iron, oxygen, carbon, nitrogen,hydrogen, yttrium, and others. Similarly, commercially pure titanium(CP-Ti) can generally be at least 99.2 wt% titanium. In some examples,the starting material for the methods described herein can be a solidtitanium material. In many examples, the starting titanium material canbe a solid article formed by any suitable process. The solid titaniummaterial can be obtained through any suitable manufacturing method. Incertain examples, the solid titanium material can be a titanium partformed by 3D printing or casting. In some cases, the solid article canbe a prior sintered article.

As used herein, “fine and ultrafine” refer to grain sizes which rangefrom about 5 µm to about 20 µm for fine grains, and less than 1 µm toabout 5 µm for ultrafine grains. Most often individual grains sizes canbe about 0.1 µm to about 8 µm in any dimension.

As used herein, the terms “dynamically controlled hydrogen atmosphere”or “dynamically controlled hydrogen partial pressure” are used to meanthat the hydrogen partial pressure can be held constant or varied as afunction of time during each step in the thermal cycle. In anyembodiment, hydrogen partial pressure can be dynamically controlled as afunction of time and temperature in order to precisely control themicrostructure of the titanium material. In particular, the hydrogenpartial pressure can be controlled during the hydrogen charging and thephase transformation stages of the methods described herein. Thehydrogen partial pressure can be controlled by the addition or removalof hydrogen from the atmosphere using mass flow controllers or pressurecontrollers. The partial pressure of hydrogen during the hydrogencharging and phase transformation can be greater than 0.01 atmosphere,and in some cases greater than 1 atmosphere. The degree of grainrefinement due to phase transformations can result from the changingphase equilibria between α, α₂, β, and δ phases of titanium and titaniumalloys during processing. These phase equilibria can change withtemperature and with equilibrium hydrogen concentration, which varies asa function of temperature and hydrogen partial pressure. Therefore, bydynamically controlling partial pressure of hydrogen as well astemperature, phase evolution and, therefore, microstructure can beprecisely controlled at each step of the process. The dynamicallycontrolled hydrogen atmosphere can have partial pressures of hydrogenbetween 0.01 atm and 10 atm, which are achieved by a mixture of hydrogenand an inert gas at approximately 1 atm to 10 atm total pressure, purehydrogen at pressures approximately between 0.01 atm and 10 atm, or afixed mixture of hydrogen and inert gas at pressures between 0.01 and 20atm. Therefore, partial pressure of hydrogen can be dynamicallycontrolled by dynamically varying the gas ratio in the former example,or the absolute system pressure in the latter two. The partial pressureof hydrogen can be controlled independently of any hydrogen that may beproduced from the evolution of hydrogen gas from hydrogenated titanium.Different hydrogen partial pressure profiles can be used to tailor themechanical properties of the as-treated material by controlling theas-treated microstructure.

As used herein, the term α phase refers to a hexagonal close-packed(HCP) solid solution of titanium with alloying elements. The α phase mayor may not contain some hydrogen. The term β phase refers to abody-centered cubic (BCC) titanium solid solution with alloyingelements, which may or may not also contain hydrogen. The term δ phaserefers to a face-centered cubic (FCC) hydrogenated titanium or titaniumhydride, TiH_(x), where x varies from 1.5 to 2, at room temperature. Theterm α₂ refers to Ti₃Al phase which is an ordered hexagonal structure inα phase with DO19 crystal structure. The definitions of the phases arefurther illustrated by the phase diagrams of Ti-H (ASM Handbook, Vol. 3,p. 238, 1992), and (Ti-6Al-4V)-H (Pei Sun et al., “An experimental studyof the (Ti-6Al-4V)-xH phase diagram using in situ synchrotron XRD andTGA/DSC techniques”, Acta Materialia, Vol. 84, pp. 29-41, 2015). Itshould be noted that the phase diagrams of titanium alloys with hydrogenvary considerably within the scientific literature and are not yetcompletely characterized. Therefore, the exact temperatures and time ofhydrogen charging, isothermal holding for phase transformation, anddehydrogenation will all vary accordingly. For example, it is noteworthythat β transus temperatures vary as a function of hydrogen content (e.g.typically falling with increases in hydrogen content).

As used herein, “globularized microstructure” can be defined asmicrostructure in which a majority of the material is composed ofprimary α (α_(p)) grains that each have an aspect ratio of typicallyless than 3:1 and β phase present primarily at the triple point of theα_(p) grains.

As used herein, a “bi-modal microstructure” can be defined asmicrostructure in which a majority of the material is composed of amixture of two types of microstructure: the first type is α_(p) grainsthat have a low aspect ratio of typically less than 3:1 and the secondtype is colonies of lamellar α grains with retained β phase. The volumefraction of either microstructure type in a bi-modal microstructure canvary from 5% to 95%, which depends on the maximum temperature andcooling rate used during the heat treatment.

As used herein, a “grain colony” is a lamellar structure generallyhaving from two to about ten parallel laminar grains. Typically, thelaminar grains are α and α₂ grains.

As used herein, the term “about” is used to provide flexibility andimprecision associated with a given term, metric or value. The degree offlexibility for a particular variable can be readily determined by oneskilled in the art. However, unless otherwise enunciated, the term“about” generally connotes flexibility of less than 2%, and most oftenless than 1%, and in some cases less than 0.01%.

As used herein with respect to an identified property or circumstance,“substantially” refers to a degree of deviation that is sufficientlysmall so as to not measurably detract from the identified property orcircumstance. The exact degree of deviation allowable may in some casesdepend on the specific context.

As used herein, the term “at least one of” is intended to be synonymouswith “one or more of.” For example, “at least one of A, B and C”explicitly includes only A, only B, only C, and combinations of each.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the elements (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Additionally, the terms andexpressions employed herein have been used as terms of description andnot of limitation, and there is no intention in the use of such termsand expressions of excluding any equivalents of the features shown anddescribed or portions thereof, but it is recognized that variousmodifications are possible within the scope of the invention claimed.Additionally, the phrase “consisting essentially of” will be understoodto include those elements specifically recited and those additionalelements that do not materially affect the basic and novelcharacteristics of the claimed invention. The phrase “consisting of”excludes any element not specifically specified.

The present disclosure is not to be limited in terms of the particularembodiments described in this application. Many modifications andvariations can be made without departing from its spirit and scope, aswill be apparent to those skilled in the art. Functionally equivalentmethods and apparatuses within the scope of the disclosure, in additionto those enumerated herein, will be apparent to those skilled in the artfrom the foregoing descriptions. Such modifications and variations areintended to fall within the scope of the appended claims. The presentdisclosure is to be limited only by the terms of the appended claims,along with the full scope of equivalents to which such claims areentitled. It is to be understood that this disclosure is not limited toparticular methods, reagents, compounds, or compositions, which can, ofcourse, vary. It is also to be understood that the terminology usedherein is for the purpose of describing particular embodiments only, andis not intended to be limiting.

As will be understood by one skilled in the art, for any and allpurposes, particularly in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the likeinclude the number recited and refer to ranges which can be subsequentlybroken down into subranges as discussed above. Finally, as will beunderstood by one skilled in the art, a range includes each individualmember.

Any steps recited in any method or process claims may be executed in anyorder and are not limited to the order presented in the claims.Means-plus-function or step-plus-function limitations will only beemployed where for a specific claim limitation all of the followingconditions are present in that limitation: a) “means for” or “step for”is expressly recited; and b) a corresponding function is expresslyrecited. The structure, material or acts that support the means-plusfunction are expressly recited in the description herein. Accordingly,the scope of the invention should be determined solely by the appendedclaims and their legal equivalents, rather than by the descriptions andexamples given herein.

Thermo-Hydrogen Refinement of Microstructure of Titanium Materials

Methods are provided for refining the microstructure of titaniummaterials. Previous progress in titanium material processing has beenmade in the particular area of powder metallurgy using the hydrogensintering and phase transformation (HSPT) process. This process isdescribed in previously-filed U.S. Pat. Application No. 14/152,787 (U.S.Pat. Application Publication No. 2014/0255240). The HSPT process is apowder metallurgy process that has proven successful at producing α+βtitanium alloys (e.g. Ti-6Al-4V) with wrought-like microstructures byutilizing hydrogen-induced phase transformations during the sinteringprocess.

In contrast with the HSPT process, the revised methods described hereincan be used to refine the microstructure of titanium starting materialsin any form, not limited to powder metallurgy sintering processes, andparticularly to already formed titanium articles. For example, themethods described herein can be used to treat individual titanium powderparticles, titanium material that has already been sintered, titaniummaterial produced by casting, titanium material produced by additivemanufacturing, titanium materials produced by machining, or any otherbulk, solid titanium material. As used herein, “individual titaniumpowders” refers to loose titanium powders and does not includeun-sintered green bodies of powders made up of separate powderparticles. Furthermore, as used herein, “solid titanium material” refersto a bulk material that is consolidated into a single mass. Accordingly,an un-sintered green body made up of separate powder particles is notconsidered a solid titanium material.

Certain types of microstructures are desirable in titanium productsbecause of their strength, ductility, and other mechanical properties.For example, globularized grains or bi-modal microstructures are twotypes of microstructures that are often sought in traditional titaniumprocessing. In order to create these desirable globularized and bi-modalmicrostructures, traditional titanium processing utilizes significantdeformation of the material to allow recrystallization to occur duringthe heat treatment. This traditional method is wrought processing, whichutilizes thermomechanical processing (TMP). TMP uses both mechanicalworking and heat treatments, as the mechanical deformation drivesrecrystallization during the subsequent heat treatment. TMP is veryenergy-intensive and, therefore, costly. Furthermore, the deformationrequired during TMP means it is not feasible for use with near-net-shapeproduction techniques, such as additive manufacturing or casting.Conversely, the ultrafine size of the α colonies and the finelydispersed β phase that can result after methods described herein canallow for globularized and bi-modal microstructures to be producedwithout recrystallization. These microstructures can result fromcoalescence of the α colonies into fine globularized α grains and thecoarsening and transformation of the finely dispersed β grains. As such,the methods described herein can be very cost effective for producingtraditional wrought-like microstructures and high performance propertieswithout sacrificing the near-net-shape capabilities of manufacturingprocesses such as additive manufacturing and casting. The methodsdescribed herein can also produce several new microstructures that arenot obtainable by traditional methods.

Titanium alloys produced using additive manufacturing (AM) technologiestend to have highly anisotropic microstructures due to the uncommonthermal histories that are produced during these manufacturingprocesses. This, in turn, results in highly anisotropic properties withparticularly limited ductility in certain directions. The methodsdescribed herein can “reset” the microstructure of titanium materialproduced through additive manufacturing to eliminate these limitations.Additionally, while the methods described herein are particularlywell-suited to additive manufacturing, the methods can also be used onany bulk titanium product using the current heat treatment. Therefore,the methods can be used to improve the microstructure and properties oftitanium alloys produced by traditional techniques such as casting,which is also near-net-shape, or even wrought processing.

In various examples, the solid titanium material used as the startingmaterial for the methods described herein can be titanium or a titaniumalloy. In further examples, the material can be titanium or a titaniumalloy that is free or substantially free of hydrogen. Titanium alloyscan be made by alloying titanium metal with additional elements.Non-limiting examples of elements that can be included in titaniumalloys include molybdenum, vanadium, niobium, tantalum, zirconium,manganese, iron, chromium, cobalt, nickel, copper, aluminum, tin,silicon, gallium, germanium, carbon, oxygen, and nitrogen. In particularexamples, the titanium material can be commercially pure (CP) titaniummetal or Ti-6Al-4V alloy. The Ti-6Al-4V alloy refers to an alloy thatconsists essentially of about 6 wt% aluminum, about 4 wt% vanadium, andthe remainder being titanium. These proportions are approximate and insome examples the amounts can vary. For example, the amount of aluminumcan be from 5.5 wt% to 6.75 wt% in some examples. The amount of vanadiumcan be from 3.5 wt% to 4.5 wt% in further examples. The alloy can alsoinclude impurities of small amounts of other elements, such as iron,oxygen, carbon, nitrogen, hydrogen, yttrium, and others. Commerciallypure titanium refers to titanium that is at least 99.2% pure by weight.Impurities in commercially pure titanium can include oxygen and smallamounts of other elements. In certain examples, any of the methodsdescribed herein, including specific temperature ranges and holdingtimes, can be used specifically with Ti-6Al-4V alloy.

In some examples, the solid titanium material can be made using additivemanufacturing, sometimes referred to as 3D printing. Various methods ofadditive manufacturing have been developed and some methods are now indevelopment. Some non-limiting examples of titanium additivemanufacturing include selective laser melting (SLM), direct metal lasersintering (DMLS), powder spray printing followed by sintering, binderjetting followed by sintering, fused filament fabrication followed bysintering, and others.

Titanium parts produced by additive manufacturing can sometime have lessthan optimal material properties, such as ductility. However, themethods for refining microstructure provided herein can increase theductility of 3D printed titanium parts. In one example, a component madeof Ti-6Al-4V alloy by selective laser melting exhibited a 300% increasein ductility when the method described herein was used to refine themicrostructure of the component. The methods described herein canincrease ductility and fatigue strength by creating wrought-likemicrostructures without wrought processing. The methods utilizehydrogen-enabled phase transformations to create an ultrafine-grainedmicrostructure that can be further engineered with heat treatments.

In some examples, methods of refining the microstructure of titaniummaterial can include heating the material under a hydrogen-containingatmosphere to a temperature above the β transus temperature of thetitanium material to increase the hydrogen concentration in the materialand convert the material to a substantially homogeneous β phase. Thiscan be referred to as “hydrogen charging.” The titanium material canthen be cooled to a temperature below the β transus temperature and heldunder the hydrogen-containing atmosphere for a period of time to producean ultrafine-grained microstructure made up of multiple phases that caninclude α, α₂, β, and δ-TiH₂ phases. This can be referred to as “phasetransformation.” The titanium material can then be held under ahydrogen-free atmosphere or vacuum at a temperature below the β transustemperature to remove hydrogen from the material. This can be referredto as “dehydrogenation.” This can result in an ultrafine-grainedmicrostructure of α and β phases. This material can be used afterdehydrogenation, or the microstructure can be further engineered using aheat treating and/or aging process.

With this description in mind, FIG. 1 is a flowchart illustrating anexample method 100 of refining a microstructure of a titanium material.The method includes: providing 110 a solid titanium material at atemperature below about 400° C.; heating 120 the titanium material undera hydrogen-containing atmosphere to a hydrogen charging temperatureabove a β transus temperature of the titanium material and below amelting temperature of the titanium material, and holding for a hydrogencharging time sufficient to convert the titanium material to asubstantially homogeneous β phase; cooling 130 the titanium materialunder the hydrogen-containing atmosphere to a phase transformationtemperature below the β transus temperature and above about 400° C., andholding for a phase transformation time to produce α phase regions; andholding 140 the titanium material under a substantially hydrogen-freeatmosphere or vacuum at a dehydrogenation temperature below the βtransus temperature and above about the δ decomposition temperature, toremove hydrogen from the titanium material.

To illustrate the methods graphically, FIG. 2 is a graph of temperatureover time for another example method of refining a microstructure of atitanium material. In this method, the solid titanium material starts atroom temperature and is heated under a hydrogen atmosphere. The materialis held at a hydrogen charging temperature. In this particular example,the hydrogen charging temperature can be from about 825° C. (shown bythe solid line) to about 1605° C. (shown by the dashed line). Throughoutthe graph in FIG. 2 , the dotted lines represent maximum temperatures ineach stage of the process and the solid lines represent minimumtemperatures. It should be noted that this graph is only one example ofthe methods described herein. The temperatures used in this example aredesigned for use with Ti-6Al-4V alloy specifically. In other examples,the method may have different minimum and maximum temperatures,especially when different titanium materials are used. For example, whentitanium materials with fewer β stabilizing alloying elements are used,such as Ti-3Al-2.5V, it may be beneficial to use higher temperatureranges to accommodate for the higher β transus temperatures.Furthermore, if a titanium materials with more β stabilizing alloyingelements are used, such as Ti-6Al-2Sn-4Zr-6Mo, it may be beneficial touse lower temperature ranges to accommodate for the lower β transustemperatures. It should also be noted that for any titanium material theβ transus temperature will vary with respect to the instantaneous andlocal hydrogen concentrations within the material, and the degree bywhich the β transus varies and, therefore, by which nominal heattreatment temperature ranges vary will also be affected by the alloyingelements present in the titanium material used.

During the hydrogen charging in the example of FIG. 2 , the titaniummaterial is converted to a substantially homogeneous β phase. Duringhydrogen charging, β phase grains can be either maintained or grown. Forexample, with laser 3D printed titanium materials grains size tends tobe sufficiently small that relatively lower temperatures are sufficientto reset the microstructure. In contrast, cast and electron beam 3Dprinted articles tend to have larger prior β phase grains such that ahigher temperature can be desirable to fully eliminate prior phasestructure of the original article.

The titanium material is then cooled to a phase transformationtemperature. The β phase titanium material can optionally be firstcooled to room temperature and reheated, or directly cooled to the phasetransformation temperature. The phase transformation temperature in thisexample is from about 400° C. to about 825° C. The material is held atthis temperature under the hydrogen atmosphere to convert regions of theβ phase to an α phase, including α phase and/or α₂ phase. Typically, theα phase and/or α₂ phase forms homogenously within the prior β grains,thereby significantly refining the microstructure. The phasetransformation temperature can also be controlled to avoid substantialgrowth of α and/or α₂ phase grains or to prevent the formation of δphase, all of which will depend on the partial pressure of hydrogen inthe atmosphere during phase transformation. Optionally, initiallycooling to room temperature can force the formation of low temperatureα, α₂ and δ phases, which can first form at the surface of the material,which, in turn, may result in a microstructural gradient before thephase transformation step.

At this point, the hydrogen atmosphere is replaced with an inertatmosphere or vacuum. The material is then held at a dehydrogenationtemperature to remove hydrogen from the material. The titanium materialmay be optionally cooled to room temperature before dehydrogenation ordirectly heated or cooled to the dehydrogenation temperature. Theminimum dehydrogenation temperature in the example of FIG. 2 is 500° C.and the maximum is the β transus (approximately 995° C. forhydrogen-free Ti-6Al-4V). Alternatively, the minimum dehydrogenationtemperature can be as low as 200° C. At lower temperatures,microstructure formed in the phase transformation stage can be preservedwhile relatively higher temperatures tend to coarsen the microstructure.In certain examples, the titanium material can be used immediately afterdehydrogenation. However, the example method shown in FIG. 2 alsoincludes heat treatment and aging after the dehydrogenation. Heattreatment is performed by holding the material under the inertatmosphere or vacuum at a heat treatment temperature. The titaniummaterial may be optionally cooled to room temperature before heattreatment or directly heated or cooled to the heat treatmenttemperature. The heat treatment temperature in this example can be fromabout 750° C. to about 995° C. The material can be cooled at a varietyof cooling rates, as shown by the multiple slanted lines after the heattreatment stage in FIG. 2 . Different cooling rates can producedifferent microstructures. As a general rule, faster cooling rates tendto form a bi-modal microstructure where β phase forms acicular orlamellar α phase while globular α_(p) phase that was formed during thehold at the heat treatment temperature remains. Conversely, slowercooling rates tend to form globular α_(p) grains of most of themicrostructure with β phase retained largely at the triple pointes ofthe α_(p) grains.

After cooling, the material can optionally cooled to room temperatureand heated up to an aging temperature. Alternately, the temperature canbe ramped down directly from the heat treatment temperature to the agingtemperature. The material can be held at the aging temperature tofurther refine the microstructure. In this example, the agingtemperature can be from about 400° C. to about 700° C. By aging, thetitanium material experiences precipitation of secondary α and/or α₂phase, which can increase the strength of the material.

It should be noted that the graph in FIG. 2 shows temperature withrespect to time, but the time axis is not necessarily drawn to scale.Each of the horizontal lines at each hold temperature is shown with aline break, indicating that the time for holding the material at thathold temperature can be different than the time shown on the graph.Accordingly, hold times that appear longer on the graph may actually beshorter in some examples. Similarly, although cooling to roomtemperature can be performed between each stage, such cooling is notrequired and may simply be cooled or heated directly to the next stagetemperature.

FIG. 3 shows another example method 300 of refining the microstructureof a titanium material. This example is shown in the form of a phasediagram for a titanium material with varying amounts of hydrogen atvarying temperature. The vertical axis shows temperature in °C and thehorizontal axis shows the hydrogen content in atom percent. Thetemperature and hydrogen content of the titanium material are shown bybold dashed arrows. Thin solid or dashed lines are used to show theboundaries between different phase regions of the phase diagram, and theparticular material phases present in each region are written, such as“β” and “α + β.” In this example, the titanium material starts with 0%hydrogen (or at least less than about 0.02%) at room temperature andthen is heated to a hydrogen charging temperature 310 under a hydrogenatmosphere. The average hydrogen content of the titanium material mayincrease during the hydrogen charging step. Then, the material is cooledunder the hydrogen atmosphere to a phase transformation temperature 320.The hydrogen content of the material continues to increase during thisstage. At this point the titanium material can form portions of α and α₂phase in addition to the β phase. The material is cooled 330 to roomtemperature. As mentioned above, although the material can optionally becooled to room temperature between some of the stages in the process, inother examples the material can be ramped to the next hold temperaturewithout cooling to room temperature. Next, the titanium material isheated to a dehydrogenation temperature 340 under a hydrogen-freeatmosphere or vacuum. The hydrogen content decreases to less than0.0125%. Then, the titanium material is finally cooled 350 to roomtemperature.

In more detail, the methods of refining microstructures of titaniummaterials can begin with providing a solid titanium material at atemperature below about 400° C. In some examples, the solid titaniummaterial can be at room temperature. In further examples, the solidtitanium material can be free of or substantially free of hydrogen. Asmentioned above, the solid titanium material can be prepared by anysuitable process, including sintering, casting, additive manufacturing,machining, and so on. If the solid titanium material is prepared using ahigh-temperature process such as sintering, the solid titanium materialcan be cooled to a temperature below about 400° C. before beginning themethods described herein.

After the solid titanium material has been provided, the solid titaniummaterial can be heated to a hydrogen charging temperature under ahydrogen-containing atmosphere. As mentioned above, thehydrogen-containing atmosphere can include a partial pressure ofhydrogen gas that can be controlled. In some examples, the atmospherecan consist of or consist essentially of hydrogen gas at a desiredpressure. In other examples, the atmosphere can include hydrogen mixedwith an inert gas such as argon. In certain examples, an atmosphere ofhalf hydrogen and half argon, with respect to partial pressures, can beused.

The hydrogen charging temperature can be above the β transus temperatureand below the melting temperature of the solid titanium material.Accordingly, the hydrogen charging temperature can vary depending on themelting temperature of the particular titanium alloy. The β transustemperature is the temperature at which the material can entirelytransform into homogenous β phase. A “homogeneous β phase” refers to amaterial having greater than 99% β phase, by volume, with non-β phasematerial confined to the grain boundaries and triple points of the βgrains. The β transus temperature can vary with the hydrogen content ofthe titanium material. For example, the β transus temperature candecrease as the hydrogen content increases from 0% to a higher content.While the titanium material is held at the hydrogen chargingtemperature, hydrogen can dissolve in the entire volume of the titaniummaterial and the material can be converted to a homogeneous β phase.

In certain examples, the solid titanium material can be a sinteredmaterial having a density of 96% or greater. In some cases, the densityof such a sintered material can be increased during the hydrogencharging stage. In some examples, the density can increase to 98% orgreater, 99% or greater, or 100%. In such examples, using a higherhydrogen charging temperature can help to further densify the sinteredmaterial. In further examples, for non-sintered materials the hydrogencharging stage can help to remove any porosity or other defects that maybe in the material. In certain examples, the hydrogen chargingtemperature can be from about 1200° C. to about 1605° C. In otherexamples, the hydrogen charging temperature can be from about 825° C. toabout 1605° C. or from 825° C. to 1200° C.

The hold time for hydrogen charging, phase transformation, anddehydrogenation can each vary depending on the size of the titaniummaterial being processed and in particular a diffusion length from asurface of the material to a maximum depth from a nearest surface). As ageneral rule, materials having a greater diffusion length require alonger hold time for a given temperature. Utilizing lower temperaturescan significantly increase hold time while higher temperatures maygreatly decrease hold time. Additionally, atmospheric factors such asvacuum pumping speed, hydrogen partial pressure in vacuum, ultimatevacuum level (if using vacuum), inert gas flow rate, inert gas purity,and the like can also affect hold times desirable to achieve hydrogencharging, phase transformation, and/or dehydrogenation. Therefore, asone example, hydrogen content can be checked by inert gas fusiontechniques in accordance to industry standards (e.g. ASTM 1409) in orderto assess degree of completion for one or both of hydrogen charging anddehydrogenation stages.

In some examples, the hydrogen charging hold time can be from about 1minute to about 24 hours for diffusion lengths up to about 1.5 inches.In further examples, the hold time can be from about 1 hour to about 4hours for much smaller parts and shorter diffusion lengths (e.g. lessthan about 1 inch). In still further examples, the hold time can be fromabout 5 minutes to about 1 hour for yet shorter diffusion lengths (e.g.less than about 0.5 inch). For diffusion lengths less than 1.5 incheshydrogen charging hold times up to 10 days can be expected when using atemperature of 750° C. For diffusion lengths greater than 1.5 in,hydrogen charging hold times of 1-30 days can be expected when using atemperature of 750° C. Diffusion lengths up to about 3-4 inches and insome cases from greater than 1.5 inches to 4 inches can be refined.

The hold time can be sufficient to allow substantially the entiretitanium material to be converted to β phase. By converting the entirematerial to the β phase, any microstructure present in the initial solidtitanium material can effectively be “reset.” Accordingly, in someexamples the methods described herein can produce the same finalmicrostructure regardless of what type of microstructure the titaniummaterial had initially. In some cases, titanium parts made by additivemanufacturing can have a coarse microstructure with sub-optimalproperties. However, converting the titanium parts to a homogeneous βphase can reset the microstructure and allow for refining themicrostructure into any of the final microstructures described herein.In some cases, it may be beneficial to only partially charge thematerial during hydrogen charging to produce the final microstructuresonly near the surface of the material.

The hold time can also depend on the kinetics of hydrogen diffusion,which may vary depending on temperature, hydrogen partial pressure, andthe type of titanium alloy being processed. In some examples, the rateof diffusion of hydrogen can tend to increase with increasingtemperature. However, the solubility of hydrogen in titanium alloys mayalso decrease with increasing temperature. Accordingly, at hightemperature ranges, the solubility of hydrogen in the titanium materialmay be insufficient to allow for efficient hydrogen charging of thetitanium material. Therefore, in some examples, the hydrogen chargingstage can also include first holding the titanium material at a moderatetemperature that is lower than the hydrogen charging temperature. Thiscan “pre-charge” the titanium material with hydrogen before increasingthe temperature to the hydrogen charging temperature to convert thematerial to β phase. In certain examples, the titanium material can beheld at a pre-charge temperature from about 500° C. to about 700° C. topre-charge the material with hydrogen before heating the materialfurther to a hydrogen charging temperature from about 825° C. to about1605° C. The material can be held at the pre-charge temperature for apre-charge time. The pre-charge time can be longer for larger andthicker titanium parts. In several examples of relatively small parts upto about 1.5 inches, the pre-charge time can be from about 5 minutes toabout 24 hours, or from about 5 minutes to about 1 hour, or from about 1hour to about 4 hours.

In further examples, the hydrogen charging stage, including optionallyholding at a pre-charge temperature if desired, can last for a total ofabout 1 minute to about 48 hours, or from about 5 minutes to about 24hours, or from about 5 minutes to about 1 hour, or from about 1 hour toabout 8 hours, or from about 1 hour to about 4 hours. In still furtherexamples, the hydrogen charging stage can convert the solid titaniummaterial to a substantially homogeneous β phase. In yet furtherexamples, the hydrogen charging stage can raise the hydrogen content ofthe solid titanium material from about 0% to about 5% or greater, orfrom about 0% to about 10% or greater, or from about 0% to about 15% orgreater, by atom percent, and in some cases up to about 25 atom%.

As a further example, the hydrogen charging stage can include holding atthe pre-charge temperature for a pre-charge time under an inert gasatmosphere. Although other gases may be used, argon, helium, nitrogen orthe like can be suitable. For example, an inert gas atmosphere can beintroduced and the part heated up to the pre-charge temperature. Once atthe pre-charge temperature the material can be held for a pre-chargetime of 1 minute to about 4 hours, and in some cases 1 minute to about30 minutes. Subsequently, the hydrogen-containing atmosphere can beintroduced and held for the hydrogen charging time. As a generalguideline, the pre-charge temperature and the hydrogen chargingtemperature can be the same, or within about 50° C. of one another. Suchpre-charging can help to reduce or eliminate formation of cracks due toformation of δ phase titanium.

After hydrogen charging, the titanium material can be cooled to a phasetransformation temperature. This can also be performed under ahydrogen-containing atmosphere. In some examples, the hydrogen partialpressure can be the same during hydrogen charging and phasetransformation. In other examples, the hydrogen partial pressure can bedynamically controlled to affect the diffusion rate of hydrogen or thehydrogen content of the titanium material. The equilibrium hydrogenconcentration of titanium materials can change with temperature as wellas with hydrogen partial pressure. Therefore, it may be desirable tocontrol the hydrogen concentration as the material is cooled or heatedin order to produce a more or less uniform hydrogen concentration withinthe sample in order to produce a more or less homogeneous microstructureafter phase transformation. The phase transformation temperature can bebelow the β transus temperature and above about 400° C. The titaniummaterial can be held at the phase transformation temperature for a phasetransformation time to produce α and/or α₂ phase regions.

During the phase transformation stage, homogeneous precipitation oflower-temperature phases can occur in the β phase material. In someexamples, at least an α phase (α phase and/or α₂ phase) can precipitate.At lower temperatures, the δ phase can also precipitate. In certainexamples, the material can have an ultrafine-grained acicularmicrostructure after precipitation of these phases. In further examples,the phase transformation can form a thin layer of grain boundary α phaseat the primary β grain boundaries. This thin layer can, in someexamples, have a thickness from 0.05 µm to 5 µm.

The phase transformation time can vary from about 1 minute to about 10days, and in some cases 1 to 3 days, and in one example about 32 hours.The time can be in the range of a few minutes if the phasetransformation temperature is high, diffusion kinetics are high, and/orthe size of the titanium material sample is small (e.g. less than 1.5inches or less than 0.5 inches). In other examples, the time can be inthe range of days if the phase transformation temperature is low,diffusion kinetics are slow, or the sample is large (i.e. larger than1.5 inches to about 4 inches in maximum diffusion length). In someexamples, the phase transformation time can be sufficient to form both αphase and α₂ phase. Surprisingly, these methods of refiningmicrostructure can be effective in parts having up to about 4 inches inmaximum diffusion length within reasonable times, e.g. less than 30days. Since diffusion rates are exponential such diffusion depths wereexpected to require excessively long hold times for one or more stages.However, as outlined herein, this method can effectively refinemicrostructure up to about 4 inches using hold times of less than about10 days, and in some cases less than 30 days for each step.

During the phase transformation stage, the titanium material can pick upadditional hydrogen from the hydrogen-containing atmosphere. In someexamples, the phase transformation time can be sufficient for thetitanium material to reach a hydrogen content of 25% or greater, 30% orgreater, 35% or greater, or 40% or greater, by atom percent.

In certain examples, the titanium material can be cooled to roomtemperature after holding at the phase transformation temperature forthe phase transformation time. This can further alter themicrostructure, such as by forming δ phase grains. In other examples,the titanium material can transition directly from the phasetransformation temperature to the dehydrogenation temperature withoutcooling in between.

The titanium material can be dehydrogenated after the phasetransformation to form the ultrafine-grained microstructure consistingof α and β phases. Dehydrogenation can be accomplished by holding thetitanium material at a dehydrogenation temperature under a hydrogen-freeatmosphere or vacuum. In some examples, the hydrogen-free atmosphere canbe argon or another inert gas. This dehydrogenation can reduce thehydrogen content to below 150 ppm in some examples. In further examples,the hydrogen content can be reduced to below 10 ppm if very pure argonor high vacuum is used. As used herein, “substantially hydrogen-free”can refer to materials with less than 150 ppm by weight hydrogen.Accordingly, the dehydrogenation stage can result in a titanium materialthat is substantially hydrogen-free.

The dehydrogenation temperature can be below the β transus temperatureand above the δ phase decomposition temperature. In certain examples,the dehydrogenation temperature can be from about 500° C. to about 995°C. or from about 650° C. to about 750° C. The titanium material can beheld at the dehydrogenation temperature for a dehydrogenation time fromabout 1 minute to about 10 days, in other cases from 1 to 10 days, andin some cases up to 30 days for diffusion lengths greater than 1.5inches depending on temperature and other factors as previouslydiscussed above with respect to the hydrogen charging stage. In furtherexamples the dehydrogenation time can from about 5 minutes to about 24hours, from about 5 minutes to about 1 hour, or from about 1 hour toabout 4 hours. In some examples, the dehydrogenation time can be in therange of several days if the dehydrogenation temperature is low, if thetitanium part is large (e.g. greater than 1.5 inches in maximumdiffusion length), or if a particularly low final hydrogen concentrationis desired. The dehydrogenation time can be in the range of minutes orhours if the dehydrogenation temperature is higher, if the part is small(e.g. 1.5 inches or less diffusion length), or if the final hydrogenconcentration can be higher.

In certain examples, the microstructure of the titanium material canchange during the dehydrogenation. In one example, the microstructurecan change from an ultrafine-grained acicular microstructure to anultrafine-grained lamellar microstructure with finely dispersed β phasegrains at the triple points of lamellar α phase colonies. Thismicrostructure can have excellent strength and ductility. In furtherexamples, the microstructure changes during dehydrogenation can becontrolled by selecting the dehydrogenation temperature. At lowerdehydrogenation temperatures, such as from about 500° C. to about 650°C., the small grain size microstructure of the material can bepreserved. This can result in higher strength and thinner layers of αphase at the prior β grain boundaries. On the other hand, mid-rangedehydrogenation temperatures, such as from about 650° C. to about 800°C., can coarsen the microstructure. This can result in higher ductilityand thicker α phase layers at the prior β grain boundaries.Additionally, in some examples using a higher dehydrogenationtemperature, such as from about 825° C. to about 995° C., can result ina microstructure gradient, in which the center of the titanium part canhave a coarser, more ductile microstructure and the outer surface of thepart can have a stronger, finer microstructure. This can be caused bythe interior of the part remaining at a higher hydrogen content whilethe temperature is above the β transus temperature of the titaniummaterial with the higher hydrogen content. For example, in Ti-6Al-4Valloy, the β transus temperature of the hydrogen-free alloy can be about995° C. and the β transus temperature can go as low as about 825° C. athigher hydrogen contents. Accordingly, when the dehydrogenationtemperature is between these temperatures, the exterior surface of thealloy can give off hydrogen more quickly than the interior, so that theβ transus temperature of the exterior surface rises above thedehydrogenation temperature. At the same time, the interior of the alloycan be hotter than the β transus temperature at the higher hydrogencontent so that the β phase forms in the interior.

In some cases, the titanium material can be used as it is immediatelyafter the dehydrogenation stage. As explained above, several differentmicrostructures can be achieved by selecting appropriate dehydrogenationtemperatures. In other examples, further heat treatment and/or aging canbe performed after dehydrogenation.

Heat treatment, if performed, can include holding the titanium materialat a heat treatment temperature under an inert atmosphere or vacuum. Insome examples, the heat treatment temperature can be above about 750° C.and below the β transus temperature. In certain examples, the heattreatment temperature can be from about 750° C. to about 995° C. Thetitanium material can be held at this temperature for a heat treatmenttime from about 1 minute to about 24 hours. In some examples, the heattreatment time can be from about 5 minutes to about 4 hours, or fromabout 1 hour to about 4 hours, or from about 5 minutes to about 1 hour.

The increased temperature of heat treatment can cause the β grains togrow due to the higher equilibrium fraction of β phase at highertemperatures. In some examples, heating to the heat treatmenttemperature can also cause ultrafine-grained α colonies in the materialto coalesce to form globular primary α phase, which can be driven by thehigh grain boundary energy in the ultrafine-grained α colonies. Thismicrostructure can then be further adjusted by controlling the speed ofcooling the titanium material after heat treatment. In one example, thetitanium material can be cooled slowly to room temperature after theheat treatment. The cooling rate can be from about 1° C. per minute toabout 10° C. per minute, for example. This can result in anequiaxed/globular microstructure made up of primary α grains withresidual β contained at the primary α triple points.

In another example, the cooling rate can be high. For example, thetitanium material can be quenched in brine, water, or oil to cool thematerial very rapidly. In other examples, the cooling rate can be fromabout 50° C. to about 50,000° C. per minute. This fast cooling canresult in a bi-modal microstructure made up of primary α grains in amatrix of fine a/β that are either lamellar or acicular. Brine or waterquenching can provide the highest cooling rate, which can result in αlamellae with a higher aspect ratio, while air cooling can provide aslower cooling rate that results in α lamellae with a lower aspectratio.

In alternative examples, the heat treatment can include heating thetitanium material to a temperature above the β transus. If the materialis slowly cooled after this, a coarse lamellar microstructure can formwith lower aspect ratio α grains. Cooling quickly after this heating canform thinner α grains with a higher aspect ratio.

The methods of refining microstructures of titanium materials can alsoinclude aging the titanium material by holding the titanium material atan aging temperature from about 400° C. to about 650° C. under an inertatmosphere or vacuum. During aging, secondary α and α₂ grains canprecipitate to increase the strength of the material. The temperatureand time used for aging can depend on the particular titanium alloy andthe desired level of strengthening. Greater strengthening can beachieved by holding the material at lower temperatures for longer times,such as temperatures from about 400° C. to about 500° C. for times ofabout 1 day to about 10 days. This strengthening can also result in theloss of some ductility. In other examples, moderate strengthening can beachieved at higher temperatures, such as from about 500° C. to about650° C., with less loss of ductility. At these higher temperatures,diffusion can be faster and therefore the aging time can be shorter. Insome examples, the aging time can be from about 1 minute to about 24hours, from about 5 minutes to about 12 hours, or from about 2 hours toabout 12 hours.

In any of the above embodiments, the process can be void of mechanicalprocessing steps after hydrogen charging. As used herein, the term“mechanical processing steps” refers to forging, rolling, extrusion,drawing, swaging, and the like as known in the art. Mechanicalprocessing steps are those steps where the material is deliberatelydeformed plastically at either elevated (hot working) or roomtemperatures (cold working). In a conventional process includingmechanical processing steps, after the plastic deformation of coldworking, or during hot working the microstructure of the material can betransformed at elevated temperatures via recrystallization to achieve adesired microstructure. However, by using the processes of the presentinvention, strong titanium materials with fine microstructures can beproduced without the need for further mechanical processing steps afterthermo-hydrogen refinement.

The present disclosure also extends to the titanium materials producedusing the methods described above. In some examples, the methodsdescribed above can produce unique microstructures not obtainable byother methods. The methods described herein can transform a materialwith a coarse grained α + β titanium microstructure to anultrafine-grained lamellar, globular, or bi-modal microstructure thatcontains discontinuous β phase without any thermomechanical processing.

In some examples, the titanium metal or titanium metal alloys obtainedfrom the process can have a fine or ultrafine grain size (i.e. averagegrain size). Such ultrafine grain sizes on the microscopic scale providefor high strength and ductility in the macro scale materials. In any ofthe above embodiments, the titanium metal or the titanium metal alloyobtained from the process can have an α grain size of less than 100 µm.In some embodiments, the titanium metal or titanium metal alloy preparedusing the above process can have a grain size of less than 10 µm. Insome embodiments, the titanium metal or titanium metal alloy preparedusing the above process can have a grain size of less than 20 µm and insome cases less 5 µm. In other embodiments, the titanium metal or thetitanium metal alloy can have a grain size of from about 10 nm to about10 µm. In other embodiments, the titanium metal or the titanium metalalloy can have a grain size from about 10 µm to about 100 µm. Thesegrain sizes and other properties recited herein can be obtained directlyfrom the process without further post-processing.

FIG. 4 shows the microstructure of one example titanium material 400that can be produced using the methods described herein. Thismicrostructure can be made by cooling the material immediately followingthe dehydrogenation stage. The microstructure includes lamellar α phasecolonies 410 with β grains 420 dispersed between the α colonies. Grainboundary α 430 forms at boundaries of prior β grains (i.e. β grainsformed during hydrogen charging and β anneal/reset).

FIG. 5 shows another example microstructure of a titanium material 500.This microstructure can be made by heat treating the material and thencooling slowly, at a rate of 10° C. per minute or slower. Themicrostructure includes globularized primary α grains 510 and β grains520. As with FIG. 4 , grain boundary α 530 forms at boundaries of priorβ grains.

FIG. 6 shows yet another example microstructure of a titanium material600. This microstructure can result from quickly cooling the materialafter heat treating. The microstructure includes primary α grains 610 ina matrix of fine a/β lamellae 620. Once again, grain boundary α 630forms at boundaries of prior β grains.

In further examples, the microstructures produced using the methodsdescribed herein can be described in more detail by measuring the lengthand width of the various phase grains in the microstructures. In oneexample, a titanium material can be made by treating Ti-6Al-4V alloyusing the hydrogen charging, phase transformation, and dehydrogenationprocesses described above. The final microstructure of the material canhave the following characteristics shown in Table 1.

TABLE 1 Feature Average Minimum (µm) Average Maximum (µm) α lathe length5 8 α lathe width 0.1 2 α colony length 5 8 α colony width 1 4 GB αthickness 2 6 β length 0.5 3 β width 0.4 0.5 Prior β diameter 50 >1000

In another example, a Ti-6Al-4V alloy can be treated by the hydrogencharging, phase transformation, dehydrogenation, and heat treatmentprocesses described above. This microstructure can have thecharacteristics shown in Table 2.

TABLE 2 Feature Average Minimum (µm) Average Maximum (µm) α_(p) length 510 α_(p) width 5 10 α lathe length 5 10 α lathe width <1 <1 α colonylength 5 10 α colony width 1 4 GB α thickness 1 6

The foregoing detailed description describes the invention withreference to specific exemplary embodiments. However, it will beappreciated that various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theappended claims. The detailed description and accompanying drawings areto be regarded as merely illustrative, rather than as restrictive, andall such modifications or changes, if any, are intended to fall withinthe scope of the present invention as described and set forth herein.

What is claimed is:
 1. A method of refining a microstructure of atitanium material, comprising: providing a solid titanium material at atemperature below about 400° C.; heating the titanium material under aninert gas atmosphere to a pre-charge temperature for a pre-charge timeto form a heated titanium material; exposing the heated titaniummaterial under a hydrogen-containing atmosphere to a hydrogen chargingtemperature above a β transus temperature of the titanium material andbelow a melting temperature of the titanium material, and holding for ahydrogen charging time sufficient to convert the titanium material to asubstantially homogeneous β phase titanium material; cooling the β phasetitanium material under the hydrogen-containing atmosphere to a phasetransformation temperature below the β transus temperature and aboveabout 400° C., and holding at the phase transformation temperature for aphase transformation time to produce a transformed titanium materialhaving α phase regions; and holding the transformed titanium materialunder a substantially hydrogen-free atmosphere or vacuum at adehydrogenation temperature below the β transus temperature and aboveabout δ phase decomposition temperature for a dehydrogenation time, toremove hydrogen from the transformed titanium material to form adehydrogenated titanium material.
 2. The method of claim 1, wherein thetitanium material has a maximum diffusion length of greater than 1.5inches to about 4 inches.
 3. The method of claim 1, wherein thepre-charge temperature is within 50° C. of the hydrogen chargingtemperature.
 4. The method of claim 1, wherein the inert gas is argon orhelium.
 5. The method of claim 2, wherein the hydrogen chargingtemperature is from about 825° C. to about 1605° C. and the hydrogencharging time is from about 1 day to 10 days.
 6. The method of claim 2,wherein the phase transformation temperature is from about 400° C. toabout 825° C. and the phase transformation time is from about 1 day to10 days.
 7. The method of claim 2, wherein the dehydrogenationtemperature is from about 200° C. to about 995° C. and thedehydrogenation time is 1 day to 10 days.
 8. The method of claim 1,wherein the hydrogen-containing atmosphere consists of pure hydrogen ora mixture of hydrogen and inert gas wherein a partial pressure ofhydrogen is from about 0.5 atm to about 1 atm.
 9. The method of claim 1,further comprising heat treating the dehydrogenated titanium materialafter removing the hydrogen by holding the dehydrogenated titaniummaterial at a heat treatment temperature above about 750° C. and belowthe β transus temperature of the titanium material under an inertatmosphere or vacuum to form a heat treated titanium material.
 10. Themethod of claim 9, wherein the heat treatment temperature is from about750° C. to about 995° C.
 11. The method of claim 9, further comprisingaging the heat treated titanium material after the heat treatment byholding the heat treated titanium material at an aging temperature fromabout 400° C. to about 700° C. for at least about 2 hours under an inertatmosphere or vacuum to form an aged titanium material.
 12. The methodof claim 1, wherein the solid titanium material is a sintered materialhaving a density from about 96% to about 100%.
 13. The method of claim1, wherein the solid titanium material comprises commercially puretitanium, Ti-6Al-4V alloy, or a combination thereof.
 14. A titaniummaterial having an ultrafine-grained or fine-grained microstructure,comprising α colonies or globular α_(p) grains with diameters 10 togreater than 200 times smaller than prior β grains they were formedfrom, very fine and discontinuous β grains after refinement at thetriple points of the α colonies and α_(p) grains, and grain boundary αfound at prior β grain boundaries with a thickness that is within 50% ofan average diameter of the α colonies or α_(p) grains, and wherein thetitanium material has a maximum diffusion length greater than 1.5inches.